A sensor signal processing apparatus that processes a sensor signal output from a sensor generally has a configuration including an oscillator. Further, the oscillator used in the sensor signal processing apparatus usually has a configuration including a piezoelectric vibrator. Therefore, the general sensor signal processing apparatus has a configuration including a semiconductor integrated circuit and a piezoelectric vibrator externally attached to the semiconductor integrated circuit.
In the semiconductor integrated circuit described above, for example, there is a demand that a primary battery is used as a power source for the semiconductor integrated circuit and the semiconductor integrated circuit can be operated for a long period of time (for example, 10 years or the like) without replacing the battery. In order to satisfy such demand, it is necessary to reduce the power consumption of the semiconductor integrated circuit.
As a method for achieving low power consumption of the semiconductor integrated circuit, intermittently operating the semiconductor integrated circuit is considered. In the case of intermittently operating the semiconductor integrated circuit, the more the low power consumption is promoted, the longer a period during which the operation of the semiconductor integrated circuit is stopped. Therefore, in the case of intermittently operating the semiconductor integrated circuit, it is important that the semiconductor integrated circuit does not adversely affect a piezoelectric vibrator when the operation of the semiconductor integrated circuit is stopped, in order to prolong a lifespan of the piezoelectric vibrator externally attached to the semiconductor integrated circuit.
In some cases, a sensor such as an acceleration sensor or an angular velocity sensor incorporates a piezoelectric vibrator or a silicon vibrator formed by using a micro electro mechanical systems (MEMS) technology therein and performs sensing using vibration of the vibrator, the semiconductor integrated circuit includes an oscillation circuit that oscillates the vibrator incorporated in the sensor, and the sensor signal processing apparatus processes a sensor signal output from the sensor. In these cases, it is also important that the semiconductor integrated circuit does not adversely affect the vibrator incorporated in the sensor when the operation of the semiconductor integrated circuit is stopped, in order to prolong a lifespan of the vibrator incorporated in the sensor and externally attached to the semiconductor integrated circuit.